Additive for dielectric fluid of transformer assembly



June 23, 1959 T.'.K. SLOAT ET AL 2,892,166

ADDITIVE FOR DIELECTRIC FLUID OF TRANSFORMER ASSEMBLY Filed Jan. 20, 1955 Fig. l.

Fig.2.

WITNESSES INVENTORS James 6. Ford 8 Truman K. Sloci United States Patent Ofice ADDITIVE FOR DIELECTRIC FLUID OF TRANSFORMER ASSEMBLY Application January 20, 1955, Serial No. 483,104 3 Claims. (Cl. 336-94) Mercer County, Pa., assignors to Westing- East Pittsburgh, Pa., a cor- The present invention relates to dielectric fluids and has particular reference to electrical apparatus insulated with dielectric fluids comprising mineral oil. Mineral oil is used extensively as a dielectric fluid in electrical apparatus such as transformers, capacitors, regulators, bushings, switches, cables and the like. It has been observed that such oil insulated electrical apparatus sometimes shows a decided increase in power factor-after having been in service for varying periods of time. This has been observed primarily in transformers; for example, in which the ratio of insulation to oil is very high and especially in those transformers which are completely sealed from oxygen and operate at temperatures below 60 C. Thus, some transformers which have a power factor of about 1-2% when manufactured have been found to have power factors as high as 30% after being in service for some months. This power factor increase can be determined either by testing'the entire transformer unit or by testing the oil alone.

This undesirable increase in power factor occurs in spite of great care being exercised in the manufacture of such oil-filled electrical apparatus. In the manufacture. of current and voltage instrument transformers, for example, the oil is carefully degassed and the transformer is vacuum filled with such degassed oil. The transformer units themselves are enclosed in welded cases and the tube through which oil is introduced into the case is sealed ofl to insure that the transformer is air-tight. Thus, there is no chance for entry of air, moisture or deleterious external material, nor for escape of any volatile oil products or any gaseous insulation components. Notwithstanding all these precautions some of the transformers do exhibit an increase in power factor after they have been in service for a while. 7

The reason for such increasesin power factor is not fully understood at this time but it is believed to be caused 'by certain weakly charged particles present in the solid insulating materials used in the manufacture of the transformer itself. Such particles may be characterized as polar-type contaminants which may become dissolved in or dispersed throughout the mineral oil with the result that, by some unknown mechanism, an increase in power factor occurs.

We have made the surprising discovery that certain additive material in combination with mineral oil provides a dielectric fluid which when incorporated in electrical apparatus prevents an undesirable increase in power factor of such oil and apparatus even after said apparatus has been in service for extended periods of time.

The object of the present invention is to provide for stabilizing dielectric fluids comprising mineral oil, by combining 8-hydroxy quinoline therewith.

,Another object of this invention is to provide electrical apparatus insulated with a dielectric fluid com- 2,892,166 Patented June 23, 1959 2 prising a major proportion of mineral oil and a minor proportion of 8-hydroxy quinoline.

Other and further objects of the invention will, in part, be obvious and will, in part, appear hereinafter.

For a fuller understanding of the nature and objects of this invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawing in which:

Figure 1 is a view in elevation, partly in section, of a transformer;

Fig. 2 is a view in elevation, partly in section, of a capacitor; and

Fig. 3 is a fragmentary view, partly in section, of a cable.

We have discovered that mineral oil used as a-fluid dielectric in electrical apparatus may be improved by incorporating therein a minor amount of additive material comprising 8-hydroxy quinoline. Electrical apparatus insulated with the dielectric fluid of this invention does not exhibit an undesirable increase in power factor even after such apparatus has been in use for long periods of time. It has been determined that only minor amounts of the additive material need be incorporated in the mineral oil to achieve the surprising results herein described. For example, the addition of 8-hydroxy quinoline in amounts as small as 0.01% and up to 0.1% by weight based on the total weight of the dielectric fluid, gives the desired effects described. A higher proportion of S-hydroxy quinoline of up to about 2% of the weight of the oil may be employed. As much as 2.35% by weight may be introduced, but this is the limit of room temperature solubility and at low temperatures some of the 8-hydroxy quinoline will precipitate out. Exceptionally satisfactory results have been attained when 0.04% by weight of 8-hydroxy quinoline, based on the total weight of the dielectric composition, is incorporated in a mineral oil dielectric fluid used in electrical apparatus.

It is an important feature of the present invention that the additive material herein described may be incorporated in the mineral oil either at the factory during manufacture of the electrical apparatus or in the field after such apparatus has been placed in service. In the latter instance it has been found convenient to admix the S-hydroxy quinoline in a high concentration in a carrier such as transformer oil. Also, at this time, an oxidation inhibitor such as ditertiary butyl paracresol may be added. The resulting mixture may be packaged in suitable containers, for example, glass jars or bottles, for convenient addition to transformers in the field.

The ditertiary butyl paracresol is not necessary for and plays no part in the power factor correction. The use of this material as an oxidation inhibitor for insulating oil is well known in the art and often, when power factor correction is made, it also is desirable to simultaneously inhibit the oil against oxidation. The ditertiary butyl paracresol may be used in amounts within the range of 0.1% to 0.5% by weight, and preferably in a quantity amounting to about 0.2% by weight of the dielectric composition.

As an example of power factor correction of a transformer in the field containing approximately 7 /2 gallons of mineral oil, there is introduced into the transformer casing a solution containing 10 grams of 8-hydroxy quinoline and 50 grams of ditertiary butyl paracresol dissolved in 375 grams of mineral oil, a total of approximately one pint by volume. This results in concentrations of 0.04% by weight of 8-hydroxy quinoline and 0.2% by weight of ditertiary butyl paracresol in the treated transformer. oil.

While 8-hydroxy quinoline, when in admixture with mineral oil, prevents an undesirable increase in power factor, it has been determined that certain other additives will, when admixed with mineral oil, also help to prevent such a power factor increase. It is to be understood, however, that such additional materials are not as satisfactory in this respect as is S-hydroxy quinoline. Propionic acid, dimethyl glyoXirne, and p-amino phenol have been found to be relatively good additives and naphthyl amine and 2,3ebutanedione-Z-methoxime have fairly good properties in this respect.

Tables I and II set forth data obtained on power fac tor tests made on numeraus transformers in service in the field. In Table I, the particular transformers each were filled with 7 /2 gallons of mineral oil when manufactured. Power factor tests were made on these transformers after they had been in use for varying periods of time. Thereafter, one pint of a solution of 8-hydroxy quinoline, ditertiary butyl paracresol, and mineral oil, in proportions similar to those of the preceding example, was added to the oil in the transformer. The materials were added in amounts such that the 8-hydroxy quinoline constituted 0.04% by weight and the ditertiary butyl paracresol constituted 0.2% by weight of the total dielectric composition in the treated transformer oil. Power factor determinations then were made on each of the transformers 30 to 60 days after the addition of the S-hydroxy quinoline-ditertiary butyl paracresol-mineral oil solution. The data in the tables in the column headed Overall represent the power factor determination of the transformer and dielectric fluid together. The data in the column headed Interwg represent the power factor of the transformer components separate from the oil. The column headed Oil only contains power factor data on the oil alone. The column headed Kilovolts breakdown oil dielec. contains data on the dielectric breakdown strength in kilovolts (0.1 inch gap) of the dielectric oil composition in the transformers.

TABLE I Percent power factor Kilovolts Transformer No. Overall Interwg Oil Break- Only down 011 Dielec.

{ilvithout additive 4. 5 4. 5 8. 7 28. 6 Plus additive 0. 95 1.0 O. 74 31. 6 {Without additive--. 1. 5 1. 7 3. 32. 4 Plus additive 0.88 1. O. 4.0 3 Without additive. 2. 7 1. 5 3. 7 28 Plus additive. 0. 89 0. 22 0. 5S 4 Without additiv 12. 4 13.0 18. 6 28. 3 Plus additive. 1. 4 0. 4 1 1. 3 34. 4 Without additive- 2.1 2.0 4. G 80. 6 Plus additive 0. 69 0. 74 0. 34 3 1. 5 Without additive. 1. 8 1. 9 3. 8 32 Plus additive 0.82 l. 2 0. 34 34. 5 {Without additive- 1. 4 1.1 0. 9 18 Plus additive. 0. 69 0v 72 0. 56 31. 6 {With0ut additiv 1. l 1. 5 0. 7 31. 2 Plus Additive... 0.61 0. 74 0. 56 32 {Without additive-.. 1. 8 1. 5 1. 1 30. 4 Plus Additive 0. 51 0. '7 7 0. 051 33 1 Without additive... 4. 3 4. 2 4. 9 21). 3

Plus Additive-.. 0.88 1. 2 0. 56 29 Without; additive 1. 1 1. '1 l. l 32. 8

. 69 .96 33. 0 0. 79 1. 2 0.71 33 l. 6 2. l l. 3 25. 6 0. 56 1.3 0.05 34. 9 1. 0 1.0 .5 1 32.2 0. 6 0.7 0.21 35. 1

Table 11 contains data similar to that set forth in Table I, with the exception that the transformers tested contained 15 gallons of mineral oil and had added thereto two pints of additive material comprising EhydroXy quinoline, ditertiary butyl paracresol, and mineral oil. The dielectric fluid, after addition of the two pints of additive material, contained 0.04% by weight, based on the. total weight of the dielectric fluid, of S-hydroxy TABLE II Percent power factor Dielectric Overall Transformer No.

Interwg Pomona 00 H1 The blank spaces indicate no tests were run.

The invention now will be described with reference to the accompanying drawing which illustrates the incorpo ration of the additive material of this invention in mineral oil dielectric fluids used in three different pieces of electrical apparatus.

Fig. 1 is a view in elevation, partly in section, of a transformer 10 having a casing 12 and a hermetically sealed cover 14 fitted thereto. Within the casing 12 there is disposed electrical coils and core 16 immersed in a dielectric liquid 18. The dielectric 18 comprises mineral oil and S-hydroxy quinoline and, if desired, it may contain ditertiary butyl paracresol.

Fig. 2 illustrates a capacitor 19 having casing 20 and a hermetically fitting cover 22 applied thereto. The metallic electrodes 24 are composed of a sheet metal such as aluminum or copper foil and are separated from one another by a plurality of layers of paper or other suitable insulating solid material 26. The dielectric liquid 28 in which the electrodes 24 and insulation 26 are immersed is composed of mineral oil, S-hydroxy quinoline and ditertiary butyl paracresol.

The additive material of this invention, in admixture with mineral oil, may be applied to cable insulation. Looking next at Fig. 3 of the drawing there is illustrated a cable 30 comprising a conductor 32 about which there is applied a wrapping 34 of paper, polyethylene, asbestos, or other insulation impregnated with a mixture of mineral oil and S-hydroxy quinoline. A minor amount of ditertiary butyl paracresol also may be included within theimpregnating solution. The sheath 36 of lead or other suitable metal maintains a proper hermetic condition for the impregnated insulation 34.

While the present invention has been described with reference to particular embodiments thereof it will be understood, of course, that certain changes, modifications, and substitutions may be made therein without departing from its true scope.

We claim as our invention:

1. A fluid dielectric composition adapted for use in high voltage electrical apparatus, consisting essentially; of a mineral oil, from 0.01% to 0.1% by weight of 8- hydroxy quinoline, and from 0.1% to 0.5% by weight of ditertiary butyl paracresol based on the total weight of the composition, said ditertiary butyl paracresol and said 8-hydroxy quinoline cooperating with the other components of the fluid dielectric and with the electrical apparatus to prevent a substantial increase in the power factor of said apparatus during use.

2. An electrical apparatus comprising in combination an electrical conductor and a dielectric fluid applied to the conductor, the dielectric fluid consisting essentially of a mineral oil, from 0.01% to 2.35% by weight of 8- hydroxy quinoline, and from 0.1% to 0.5% by Weight of ditertiary butyl paracresol based on the total Weight of the dielectric fluid, said ditertiary butyl paracresol and said 8hydroxy quinoline cooperating with the other components of the fluid dielectric and With the apparatus to prevent a substantial increase in the power factor of said apparatus during use.

3. An electrical transformer comprising in combination electrical coils and a core immersed in a dielectric liquid consisting essentially of a mineral oil, from 0.01% to 0.1% by Weight of 8-hydroXy quinoline, and from 0.1% to 0.5% by Weight 01": ditertiary butyl paracresol based on the total weight of the composition, said ditertiary butyl paracresol and said S-hydroxy quinoline cooperating with the other components of the fluid dielectric and with the electrical apparatus to prevent a substantial increase in the power factor of said apparatus during use.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Assaf: Ind. and Eng. Chem., August 1943, Vol. 35, #8, pp. 909-916. 

